1. Field of the Invention
The present invention relates generally to a slide adjuster attached to a seat of, for example, an automotive vehicle for adjusting the position of the seat in the longitudinal direction of the automotive vehicle and, in particular but not exclusively, to a stepless slide adjuster having a safety lock, which can adjust the longitudinal position of the seat steplessly and with which the seat can be emergency-locked, while the seat is in an unlocked state, that is, when the locking of the seat is released.
2. Description of the Related Art
A conventional seat sliding device is, for example, the step-sliding seat slide adjuster disclosed in Japanese Patent Publication (examined) No. 62-61462. This adjuster slides the seat while two locking plates alternately engage with a plurality of latches formed in a latch plate, so that one locking plate is always engaging with one of the latches while sliding the seat.
Japanese Utility Model Publication (examined) No. 62-42834 discloses a seat sliding device locking the seat using inertia. In this seat sliding device, locking portions are provided independently at two positions on the left and right sides. One of these locking portions is used as a manual lock when the seat is moved normally, and the other one is an inertial lock, which automatically locks the seat when there is an abrupt change in acceleration or deceleration of the vehicle, such as during a collision of the vehicle.
Japanese Utility Model Publication (examined) No. 63-46258 discloses a locking device for a seat sliding device provided with oblique faces before and behind locking holes, so that the locking plates are easily drawn into the locking holes.
Of the conventional devices mentioned above, the seat slide adjuster disclosed in Japanese Patent Publication No. 62-61462 requires that the seat is moved back and forth while operating the operating lever for one pitch at a time, which makes the operation of the operating lever cumbersome and requires a lot of time for the moving of the seat.
The device disclosed in Japanese Utility Model Publication No. 625-42834 has a mechanism for immediately locking the locking plates with a G-sensor (acceleration sensor), but this does not work during the operation of the locking lever.
In the locking device disclosed in Japanese Utility Model Publication No. 63-46258, when the acceleration of the seat is changed while the position of the seat is being adjusted, there is no guarantee that the locking plates are securely drawn along the oblique faces into the locking holes.
The present invention has been developed to overcome the above-described disadvantages.
It is accordingly an objective of the present invention to provide an inexpensive stepless slide adjuster having a safety lock, with which the position of a seat provided, for example, in a vehicle can be adjusted swiftly and steplessly, and with which the seat can be reliably emergency-locked while it is in the unlocked state.
In accomplishing the above and other objectives, the stepless slide adjuster having a safety lock according to the present invention includes a first member and a second member, which can move relatively to each other, a nut fastened to the first member, a screw rotatably attached to the second member and screwed into the nut, a manual locking device for manually locking the screw, and an emergency locking device having a brake drum and brake shoes for emergency locking the screw.
In the above-described construction, the lead angle of the nut and the screw is larger than the friction angle therebetween, and when the locking with the manual locking device is released, and the screw rotates with an acceleration or a speed that exceeds a predetermined value, then the brake shoes spread and frictionally engage the brake drum, thereby impeding a relative movement between the first member and the second member.
Because the lead angle of the nut and the screw is larger than the friction angle therebetween, the position of the second member with respect to the first member can be adjusted swiftly and steplessly. Moreover, the second member locks securely when the vehicle body is subjected to a large acceleration due to, for example, a collision of the vehicle while the slide adjuster is in the unlocked state, that is, the locking with the manual locking device has been released.
The stepless slide adjuster further includes a cam fastened to the screw, wherein the brake shoes are caused to spread out by way of the cam.
This construction simplifies the configuration of the emergency locking device, making it possible to provide an inexpensive stepless slide adjuster having a safety lock.
The stepless slide adjuster further includes a plurality of rollers arranged between the brake shoes and the cam.
By this construction, when the screw rotates with a rotational acceleration that is higher than a predetermined value, the brake shoes move slightly in the circumferential direction with respect to the cam, and the brake shoes are spread by the rollers and pushed against the brake drum, so that the screw can be securely emergency-locked.
Conveniently, the manual locking device includes a brake ring fastened to the screw, and a locking member for frictionally engaging with the brake ring.
This construction simplifies the configuration of the manual locking device, making it possible to provide an inexpensive stepless slide adjuster having a safety lock.